Within this application several publications are referenced by arabic numerals within parentheses. Full citations for these references may be found at the end of the specification immediately preceding the claims. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains.
This invention relates to integrated fiber optic couplers for VHSIC/VLSI interconnects and methods of making the same.
The performance of VHSIC/VLSI circuits is limited by the communication capacity between gates, chips and boards (1). A significant limitation of electronic interconnection is known as the "pinout" problem. Recent advances in circuit technology allow for up to 100,000 gates on a single chip. According to Rent's rule, a circuit with 100,000 gates requires 2,000 interconnections (2). However, the perimeter of a typical 10 mm by 10 mm chip provides space for a maximum of 300 pins, a gross undersupply (3). Stated differently, the minimum allowed pin spacing to avoid signal cross coupling is approximately 100 .mu.m, whereas Rent's rule implies a required maximum spacing of 20 .mu.m (2).
Fiber optic interconnects are recognized as a potential solution to the pinout problem and other problems arising from limitations in communication capacity (2-7). The advantages of optical over electronic interconnections include immunity to mutual interference, freedom from capacitive loading and freedom from planar contraints (5). Optical interconnections also have the potential for reconfigurable switching and optically controlled electronic logic (2).
No satisfactory means presently exists of coupling a fiber to a detector on a VLSI chip. Additionally, optical interconnections must achieve a connection spacing of less than 20 .mu.m to overcome the electrical pinout problem. A 20 .mu.m interconnection spacing would be difficult to achieve using standard fiber coupling techniques such as silicon V-groove or butt-coupling because the cladding diameter of typical optical fibers is greater than 100 .mu.m. Furthermore, butt-coupling may be mechanically unstable, provide poor alignment and is not suited for high packing densities. V-groove coupling is not easily aligned with a detector array on a chip, and gives rise to problems associated with multigroove splicing (8).